The long-term objective is to isolate and characterize proteins and enzymes important for photoreceptor functions, with special emphasis on those proteins that cause autoimmune diseases in the eye. We are interested in disease-inducing autoimmunogens on the ground that these proteins, because of their specific localization to the photoreceptors, must be unique and important to photoreceptor structure and function. Attention is particularly focused on S-antigen (S-Ag), a retina-specific antigenic protein which induces experimental autoimmune uveitis (EAU) in animals. The proposal has three specific aims: (1) Investigate the structure, properties, and distribution of S-Ag, and characterize antigenic and uveitogenic determinants of the antigen. The methods include purification of S-Ag on antibody-affinity columns, chemical and enzymic cleavage of the antigen, and characterization of peptides by HPLC, peptide mapping, and immunopathogenicity tests. (2) Examine the biochemical mechanism of S-Ag-induced EAU, especially a possible role of superoxide anion (O-2) in the inflammatory process leading to tissue damage. According to the current hypotheses, O-2 may have a direct damaging effect via OH radical formation or, alternatively, it may accentuate tissue damage by producing chemotactic agents for phagocytes. These hypotheses will be tested with proper tissue (and cell) culture systems and with a modified Boyden chamber. Cyclosporin A is a potent immunosuppressant and is known to inhibit the action of T-cells and effectively prevent the onset of EAU in S-Ag-immunized animals. Polynactins are a group of compounds which have a basic structure similar to cyclosporin A. To extend our preliminary findings on the immunosuppressive effects of polynactins, the mechanism by which polynactins suppress S-Ag-induced EAU in rats will be studied. (3) Determine the functional identity of S-Ag in the photoreceptor. The rod photoreceptor contains two rhodopsin kinases which seem to be distinct from each other. One of the kinases is very similar to 48K protein. Whether S-Ag is identical with a rhodopsin kinase (48K protein?) will be determined. The methods include isolation of these proteins and comparison by enzymic assays, peptide mapping, and uveitogenicity tests.